According to the state of the art, sphalerite containing ores or concentrates are submitted to a roasting step wherein the ore or concentrate is oxidized at an elevated temperature. In this roasting step, zinc sulfide is converted to zinc oxide while liberating SO.sub.2 and heat. subsequently zinc oxide is leached to bring it into solution. This traditional flowsheet has several disadvantages: the S0.sub.2 has to be further processed and results in a high amount of sulfuric acid. Also, the leaching which is carried out in sulfuric acid, normally necessitates two steps, whereby in a first step the ore or concentrate is submitted to neutral leaching and, in a second step, the remaining zinc ferrites are conducted to strong acid leaching. The iron which has dissolved during the strong acid leaching is precipitated, depending upon the method, as jarosite, goethite or hematite.